Block CO₂-Polycarbonates: Tunable Chain Extension with Zn(II) Carboxylates

Low molecular weight α,ω-dicarboxylic acid triblock polymers, featuring polycarbonate blocks flanking a central polyester block, are synthesized and assembled into dynamic halatopolymers via Zn(II) coordination. The number of chains coupled through Zn(II)-carboxylate interactions is tuned by using 4-tert-butylbenzoic acid (tBBA) as a sterically hindered capping ligand. Reducing tBBA content vs polymer and zinc content increases the number of junctions connected and the effective halatopolymer molar mass, leading to polymers with higher zero-shear viscosities, slower relaxation dynamics, and more pronounced elastic behavior. Temperature ramp, time-temperature superposition, and creep recovery experiments confirm enhanced dimensional stability and reduced flow under load as the degree of chain coupling increases. In the absence of Zn(II), the polymers display purely viscous behavior, highlighting the critical role of reversible metal-ligand interactions in network formation. This strategy provides a modular route to convert synthetically accessible, renewably sourced, low molar mass polymers into tunable, functional materials, offering a design platform for a new generation of polymeric materials.